Mask and wafer diffraction grating alignment system wherein the diffracted light beams return substantially along an incident angle

摘要

The present invention provides a grating-grating interferometric wafer alignment system, sensor and method for microlithography. It includes: (1) an electromagnetic radiation source with collimating optics delivering a collimated beam of a coherent single or multiple discrete wavelengths or in some cases broadband electromagnetic radiation; (2) a detector of the intensity of the collimated return electromagnetic radiation; (3) x- and y-oriented independent linear gratings for the mask-mark; (3) a "checkerboard pattern" grating for the wafer-mark; and (4) software including an algorithm for determining alignment from the return electromagnetic radiation intensity measured as a function of the relative position of the wafer and mask grating, and a means such as a Fourier transform determining phase and amplitude of a known frequency component of the intensity. In one embodiment a laser diode is used and the backscatter from the mask and wafer gratings is returned to the laser diode creating a beat signal used to determine alignment of the mask and wafer. Alignment accuracy is increased and made more tolerant of processing variables such as wafer topography and coatings.